Vallejo Marina's tiny oysters seen as 'a good sign'

U.S. Fish and Wildlife biologist Michael McGowan counts small oysters on the underside of a float at the Vallejo Marina. The small oysters are not normally found this far northeast, which McGowan believes is a testament to the quality of the water in the area.

The Vallejo Municipal Marina is home to a surprising and unprepossessing visitor: native oysters.

With about 100 tiny oysters found glommed on to the bottom of a 2-foot by 4-foot foam dock float, Vallejo won't, however, be taking over for the recently evicted Drakes Bay Oyster Co. in Point Reyes.

"It's legal to hunt native oysters if you have a fishing license," said marine biologist Michael McGowan, who discovered the oysters. "But eating the ones from the Bay system is not necessarily recommended -- and it's a lot of work."

McGowan, who has spent his days at the Marina overseeing the impact of marina dredging on endangered Delta smelt since early October, said he casually discovered the population when a dredger knocked a buoy loose.

Prior to finding a surprisingly dense collection of the oysters on the float and several others, McGowan said he was unaware they were there, because none were visibly attached to rocks around the marina, another favorite roosting ground.

"I think it's a good sign," McGowan said of finding the oysters on the last day of dredging last week. "The way they're managing the marina, it's clean enough for them to live."

Native oysters, which can generally grow to sizes between a third of an inch and an inch and a half across, require a mix of fresh and salt water. In the greater Bay Area system, waterways as far north and east as Vallejo tend to be something of the shellfish's outer reaches, said San Francisco State University research associate Andy Chang.

"They do play a key role," Chang said of the oysters' presence. "They form sort of a foundational structure for a community... they form part of the base of the food chain. They also filter out the water. In general, they've been known to provide local diversity to the (ecosystem.)"

However, the native oyster population growth and decline, associated with water salinity, can change from season to season and year to year, Chang said.

"Historically, I think oysters have been recorded in the Carquinez area in fairly high densities," Chang said. "So it's not surprising to me that we still find them in Vallejo, especially, at the mouth of the Carquinez Strait."

Chang's studies with the San Francisco Bay National Estuarine Research Reserve include a focus on how the local oyster population is influenced by the environment, among other work.

Native oysters are affected by what happens upstream -- like when fresh water is diverted from their normal pathways, salinity increases, allowing them to creep further up, Chang explained. Drought conditions, too, increase water salinity. On the other hand, changing climate conditions and global warming can bring on harsh winter rainstorms, like the region is experiencing now, which reduces salinity and makes areas less oyster-hospitable, Chang added.

"They spend their entire life in one place -- they have to take whatever is coming down the river," Chang said.

Contact staff writer Jessica A. York at (707) 553-6834 or jyork@timesheraldonline.com. Follow her on Twitter @JYVallejo.